As is known, most caps for containers, especially if destined to contain liquid foods, are provided with a guarantee seal, having weakened portions which as result of unscrewing of the container cap, break, emphasizing the fact that the container has already been opened.
However, sometimes the user does not take much notice of the effective condition of the guarantee seal. For the user to realize that the guarantee seal is broken, it is often necessary to upturn the container or bottle and carefully inspect the appearance of the seal. This means that the conditions of the guarantee seal are not immediately visible to the user, who only sporadically or randomly performs such control.